In recent years, the spread of IC cards is being promoted, and accordingly the reduction of the thickness thereof is demanded. Thus, it is now needed to reduce the thickness of semiconductor chips from the conventional about 350 μm to 50–100 μm or less.
It is common practice to grind a wafer back after the formation of a circuit pattern on a wafer surface. The grinding of the wafer back is performed while a pressure sensitive adhesive sheet is stuck to the circuit surface to thereby protect the circuit surface and fix the wafer. Pressure sensitive adhesive sheets comprising a soft substrate coated with a pressure sensitive adhesive are commonly employed in this use. However, in these pressure sensitive adhesive sheets based on a soft substrate, the tension applied at the adhesion is stored as a residual stress. When the wafer has a large diameter or is ground to an extremely small thickness, the residual stress of the pressure sensitive adhesive sheet surpasses the strength of the wafer with the result that the wafer is warped by the force exerted to cancel the residual stress. Further, after the grinding, the brittleness of the wafer, when supported by a soft substrate, has caused wafer breakage during the carrying of the wafer. Therefore, a method comprising fixing the wafer on a hard material such as a quartz plate or an acrylic plate and grinding the wafer is being studied.
In order to cut a hard brittle material such as a printer head, a glass/epoxy substrate, a glass or a ceramic into small chips, the cutting is performed after fixing the hard brittle material on a hard support material. Pressure sensitive adhesive double coated sheets are used for fixing such a cut piece on a hard support material. However, it is extremely difficult to separate the two hard materials mutually stuck with the conventional pressure sensitive adhesive double coated sheet from each other. When a very brittle material such as a wafer is used, it has been unfeasible to be free from damaging thereof.
Therefore, there is a demand for the development of a pressure sensitive adhesive double coated sheet suitable for fixing any of semiconductor wafers and the above-mentioned various cut pieces on a hard material.
Moreover, in the processing of semiconductor wafers, a surface protective sheet and a pressure sensitive adhesive sheet for fixing a wafer are required during the back grinding and the dicing, respectively. This has been burdensome from the viewpoint of process control. Further, the brittleness of the wafer has caused wafer breakage during the carrying of the wafer between the above process steps.
Therefore, there is also a demand for the development of a process enabling performing a sequence of process steps including the above wafer back grinding, dicing and carrying in the same configuration, enabling facilitating process control and enabling preventing wafer breakage.
The present invention has been made in view of the above state of the prior art. The present invention provides a pressure sensitive adhesive double coated sheet which enables efficiently processing a work piece with high precision, in particular a pressure sensitive adhesive double coated sheet suitable to a process capable of producing IC chips of high thickness precision with high yield by reducing warpage and minimizing carrying breakage in the grinding of extremely thin or large diameter silicon wafers and capable of performing back grinding and dicing in the same configuration. In addition, the present invention provides a process of producing semiconductors of high reliability in which use is made of the above pressure sensitive adhesive double coated sheet.